UNIVERSITY OF CINCINNATI ENGINEERS FIND NEW METHOD
FOR DETECTING CRACKS IN AGING AIRCRAFT PARTS

Cincinnati University of Cincinnati engineers have combined
two technologies into a new method for detecting tiny cracks in
aging aircraft parts before they reach the catastrophic stage.

Graduate student Zhongyu Yan and Peter Nagy, associate
professor of aerospace engineering, will present their results at
3:15 p.m. Tuesday, Nov. 2 during the annual meeting of the
Acoustical Society of America in Columbus.

Yan and Nagy combined laser heating and ultrasonic inspection
to improve the detection of fatigue cracks by a factor of ten
over previously known methods. That's significant considering how
difficult it can be to locate early signs of cracking.

"The material is degrading on the microscopic level. You can't
really see the cracks," explained Nagy, adding that cracks move
through older aircraft parts much faster than cracks in newer
aircraft.

The researchers tested their method using a series of aluminum
and titanium specimens with cracks ranging from .5 to 1
millimeter in length and specimens with no cracks in them. Their
results indicated that the method not only found the cracks, it
could measure the difference in the severity of the cracking.

Nagy's previous work focused solely on aluminum alloys which
are typically used in the aircraft fuselage. The current project
expands that work to titanium alloys used in engine parts. Nagy
said that was a challenge, because titanium behaves differently
than aluminum. In short, titanium doesn't heat up as quickly.

"Basically, we had to slow down the inspection to accommodate
the more sluggish response from titanium, but the detection
sensitivity is almost as good as in aluminum alloys."

As a result, the new method is more time-consuming and more
expensive. So, Nagy only expects it to be used for the most
critical parts.

Nagy's research is funded under a $5 million federal program
to improve inspections of aging aircraft in the military. A
parallel program under the Federal Aviation Administration is
working to improve the safety of commercial airliners.

Nagy will also be honored during the meeting as a newly
elected Fellow of the Acoustical Society of America.